Abstract
In a survey of peach canker in widely separated areas of southern Ontario, Valsa leucostoma Fr. was recovered more frequently and consistently than V. cincta and other suspect pathogens. V. cincta predominated on only a few varieties. While some evidence was found of a seasonal influence and of effects of maturity and varietal specificity on the relative frequency of Valsa species, inconsistencies occurred. Infection of nursery stock was established, and to a considerable extent this may determine the subsequent occurrence of canker fungi in infected trees. The pathogenicity of the two Valsa species was a function of temperature. At temperatures of 60 °F and above, V. leucostoma was more pathogenic than V. cincta on young trees. At temperatures below 50 °F the latter was more pathogenic. Coniothyrium fuckelii Sacc. proved weakly pathogenic, and Fusicoccum amygdali Delacr. was not a factor of canker in southern Ontario.
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